Question

I have a very simple script that monitors a file transfer progress, comparing its actual size with the target then calculating its hash, comparing with the desired hash and firing up a few extra things when everything seems alright.

I’ve replaced the tool used for the file transfers (wget) with deluged, which has a neat api to integrate with.

Instead of comparing the file progress and compare the hashes, I only need to know now when deluged finished downloading the files. To achieve that, I was able to modify this script to my needs, but I’m stuck trying to wrap my head around twisted framework, that deluged makes use of.

To try getting over it, I grabbed one sample script from twisted deferred documentation, wrapped a class around it and attempted to use the same concept I’m using on this script I mentioned.

Now, I don’t know exactly what to do with the reactor object, since it’s basically a blocking loop that can’t be restarted.

This is my sample code I’m working with:

from twisted.internet import reactor, defer
import time

class DummyDataGetter:
    done = False
    result = 0
    def getDummyData(self, x):
        d = defer.Deferred()
        # simulate a delayed result by asking the reactor to fire the
        # Deferred in 2 seconds time with the result x * 3
        reactor.callLater(2, d.callback, x * 3)
        return d

    def assignResult(self, d):
        """
        Data handling function to be added as a callback: handles the
        data by printing the result
        """
        self.result = d
        self.done = True
        reactor.stop()

    def run(self):

        d = self.getDummyData(3)
        d.addCallback(self.assignResult)

        reactor.run()

getter = DummyDataGetter()
getter.run()
while not getter.done:
    time.sleep(0.5)
print getter.result
# then somewhere else I want to get dummy data again

getter = DummyDataGetter()
getter.run() #this throws an exception of type error.ReactorNotRestartable
while not getter.done:
    time.sleep(0.5)
print getter.result

My questions are:

1. Should reactor be fired in another thread to prevent it blocking the code?

2. If so, how would I add more callbacks to this reactor living in a separate thread? Simply by doing something similar to reactor.callLater(2, d.callback, x * 3), from my main thread?

3. If not, what is the technique to overcome this problem of not being able to starting/stopping reactor twice or more on the same process?

Answer 1

OK, easiest approach I found to this is to simply have a separate script called using subprocess.Popen, dump the statuses of the torrents and anything else needed into the stdout (serialized using JSON) and pipe that into the calling script.

Way less traumatic than learning twisted, but of course far away from optimal.